CVE-2026-66338
MEDIUM 5.4 ALL-YEARSA flaw was found in libsoup. The chunked transfer encoding parser uses a permissive parsing function for chunk sizes that silently accepts inputs violating RFC 9112, including leading whitespace, plus sign prefixes, and trailing invalid characters. When libsoup operates behind a strict frontend proxy, this parsing differential can be exploited to smuggle HTTP requests.
No known exploitation, public exploit, or elevated probability at this time. Track for changes.
Exploitation likelihood
0.3%chance of exploitation in 30 days · 21st percentile
Impact if exploited
5.4CVSS 3.1 · MEDIUM · CNA
- ConfidentialityLow
- IntegrityLow
- AvailabilityNone
What an attacker needs
- ✓Access: Reachable over the network — no local access needed
- ✓Privileges: No account or privileges required
- ✓User interaction: No user interaction needed
- ⚠Complexity: Needs a race window or specific setup
✓ lowers the bar for an attacker · ⚠ raises it
Proof of concept
No public PoC is currently catalogued.
Search for new PoCs
Search GitHub now — results may be empty or unverified.
Tracked sources are checked weekly for the full archive, including PoCs published after the original disclosure. A later release appears after a tracked source lists it and a refresh succeeds.
Affected
Products Red Hat Enterprise Linux 10 Red Hat Enterprise Linux 6 Red Hat Enterprise Linux 7 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 9 Libsoup Enterprise Linux
Weakness (CWE)
- CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N
References and research data (JSON)
Vendor product assessments
libsoup3 as a component of Red Hat Enterprise Linux 10 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/libsoup3
- none available: Fix deferred
libsoup3-devel as a component of Red Hat Enterprise Linux 10 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/libsoup3-devel
- none available: Fix deferred
libsoup3-doc as a component of Red Hat Enterprise Linux 10 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/libsoup3-doc
- none available: Fix deferred
libsoup3.src as a component of Red Hat Enterprise Linux 10 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/libsoup3?arch=src
- none available: Fix deferred
libsoup as a component of Red Hat Enterprise Linux 6 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/libsoup
- none available: Fix deferred
libsoup-devel as a component of Red Hat Enterprise Linux 6 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/libsoup-devel
- none available: Fix deferred
libsoup.src as a component of Red Hat Enterprise Linux 6 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/libsoup?arch=src
- none available: Fix deferred
libsoup as a component of Red Hat Enterprise Linux 7 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/libsoup
- none available: Fix deferred
libsoup-devel as a component of Red Hat Enterprise Linux 7 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/libsoup-devel
- none available: Fix deferred
libsoup.src as a component of Red Hat Enterprise Linux 7 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/libsoup?arch=src
- none available: Fix deferred
libsoup as a component of Red Hat Enterprise Linux 8 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/libsoup
- none available: Fix deferred
libsoup-devel as a component of Red Hat Enterprise Linux 8 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/libsoup-devel
- none available: Fix deferred
libsoup.src as a component of Red Hat Enterprise Linux 8 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/libsoup?arch=src
- none available: Fix deferred
libsoup as a component of Red Hat Enterprise Linux 9 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/libsoup
- none available: Fix deferred
libsoup-devel as a component of Red Hat Enterprise Linux 9 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/libsoup-devel
- none available: Fix deferred
libsoup.src as a component of Red Hat Enterprise Linux 9 · known affected
Vendor assessment for this product only.
pkg:rpm/redhat/libsoup?arch=src
- none available: Fix deferred
Known Affected Software Configurations
| Vendor | Product | Version range |
|---|---|---|
| Gnome | Libsoup | * |
| Redhat | Enterprise Linux | 6.0 |
| Redhat | Enterprise Linux | 7.0 |
| Redhat | Enterprise Linux | 8.0 |
| Redhat | Enterprise Linux | 9.0 |
| Redhat | Enterprise Linux | 10.0 |
All CVSS metrics
- MEDIUM 5.4 v3.1 · CNA Primary
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N - MEDIUM 5.4 v3.1 · NVD Secondary
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N - HIGH 7.2 v3.1 · NVD Primary
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
References
Exploit-tagged references (not proof of a PoC)
- https://bugzilla.redhat.com/show_bug.cgi?id=2506950 CVE record · redhat · Updated 2026-07-24T23:01:20.503Z
NVD · CVE-2026-66338 · Updated 2026-08-24T16:44:22.590
Red Hat · CVE-2026-66338 · Updated 2026-08-25T10:01:03+00:00
Advisories
- https://access.redhat.com/security/cve/CVE-2026-66338 CVE record · redhat · Updated 2026-07-24T23:01:20.503Z
NVD · CVE-2026-66338 · Updated 2026-08-24T16:44:22.590
Red Hat · CVE-2026-66338 · Updated 2026-08-25T10:01:03+00:00 - https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-66338.json Red Hat · CVE-2026-66338 · Updated 2026-08-25T10:01:03+00:00
- https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-48752 EUVD · EUVD-2026-48752
Technical & other
- https://www.cve.org/CVERecord?id=CVE-2026-66338 Red Hat · CVE-2026-66338 · Updated 2026-08-25T10:01:03+00:00
- https://nvd.nist.gov/vuln/detail/CVE-2026-66338 Red Hat · CVE-2026-66338 · Updated 2026-08-25T10:01:03+00:00
Sources: NVD · CVE.org · All sources and attribution · EPSS